1. Field of the Invention
The present invention is in the field of materials handling and more specifically relates to an apparatus for removing air from particulate solids. Typical applications include increasing the particulate solids density prior to placing the solids in a container; predensifying a solid prior to roll or plunger compaction; and replacing the air within the particulate solids by a different gas.
2. The Prior Art
Screw feeders are commonly used to feed and to convey particulate solids. More recently, screw feeders have been used to densify and to remove air from solids, but the apparatus used tended to be self-defeating. For example, in one application, a filter cloth was placed over a metal support structure that surrounded the screw feeder. A vacuum was then applied across the filter cloth. This usually resulted in a plugged filter cloth that had to be cleared by emptying the screw feeder and using a reverse air flow to clear the plugged filter. In another example, a screw feeder was used to drive a particulate solid into a cylindrical shroud closed at its end. No provision was made to allow the air to escape, and this resulted in a particulate solid filled with compressed air. When the solid was released from the compaction screw, it immediately g expanded to relieve the air pressure, and most of the compaction wa lost.
To eliminate these problems, the present inventor initially experimented with using a perforated barrel to allow the air to escape from the solids in the screw. Unfortunately, some of the solids also escaped through the perforations, resulting in an unwanted stream of fines that had to be collected and re-introduced into the screw feeder.
The disclosed apparatus addresses all of these problems and provides solids compaction, air release, and removes the air without removing solids or plugging filters. The apparatus of the present invention can also be used to replace the air or other gas originally present in the solids by a different gas.